Screw Dislocation Growth Research Articles

Screw dislocation growth defects enhancing electromagnetic wave absorption performance of GdB6

In this study, a purity of up to 98.36 wt. % GdB6 with screw dislocation growth morphology were successfully fabricated using an in-situ reaction approach. The terraced-like structure of the GdB6 enhanced the interfacial polarization and multiple interface scattering of the electromagnetic waves. As a result, the as-obtained high purity GdB6 powder presented superior electromagnetic wave absorption performance. The minimum reflection loss value can be −49.24 dB at the frequency of 13.12 GHz with a thin matching thickness of 1.44 mm. In addition, the widest effective absorption bandwidth can be up to ∼4 GHz (14–18 GHz) with a thin matching thickness of 1.25 mm. The remarkable electromagnetic wave absorption performance of GdB6 ceramics could be attributed to conductance loss and polarization loss enhanced by the screw dislocation growth defects, as well as synergistic effects with magnetic loss. The as-obtained GdB6 with synergistic dielectric loss and magnetic loss is to be a novel single-phase with excellent electromagnetic wave absorbing material, which will pave the way on the investigation of rare earth hexaborides for the ultra-high temperature environment applications.

Lateral epitaxial growth of two-dimensional organic heterostructures.

Two-dimensional organic lateral heterostructures (2D OLHs) are attractive for the fabrication of functional materials. However, it is difficult to control the nucleation, growth and orientation of two distinct components. Here we report the combination of two methods-liquid-phase growth and vapour-phase growth-to synthesize 2D OLHs from perylene and a perylenecarboxaldehyde derivative, with a lateral size of ~20 μm and a tunable thickness ranging from 20 to 400 nm. The screw dislocation growth behaviour of the 2D crystals shows the spiral arrangement of atoms within the crystal lattice, which avoids volume expansion and contraction of OLH, thereby minimizing lateral connection defects. Selective control of the nucleation and sequential growth of 2D crystals leads to structural inversion of the 2D OLHs by the vapour-phase growth method. The resulting OLHs show good light-transport capabilities and tunable spatial exciton conversion, useful for photonic applications. This synthetic strategy can be extended to other families of organic polycyclic aromatic hydrocarbons, as demonstrated with other pyrene and perylene derivatives.

Microwave synthesis of molybdenene from MoS2

Dirac materials are characterized by the emergence of massless quasiparticles in their low-energy excitation spectrum that obey the Dirac Hamiltonian. Known examples of Dirac materials are topological insulators, d-wave superconductors, graphene, and Weyl and Dirac semimetals, representing a striking range of fundamental properties with potential disruptive applications. However, none of the Dirac materials identified so far shows metallic character. Here, we present evidence for the formation of free-standing molybdenene, a two-dimensional material composed of only Mo atoms. Using MoS2 as a precursor, we induced electric-field-assisted molybdenene growth under microwave irradiation. We observe the formation of millimetre-long whiskers following screw-dislocation growth, consisting of weakly bonded molybdenene sheets, which, upon exfoliation, show metallic character, with an electrical conductivity of ~940 S m−1. Molybdenene when hybridized with two-dimensional h-BN or MoS2, fetch tunable optical and electronic properties. As a proof of principle, we also demonstrate applications of molybdenene as a surface-enhanced Raman spectroscopy platform for molecular sensing, as a substrate for electron imaging and as a scanning probe microscope cantilever.

Oriented growth of cobalt electrodeposits assisted by an interfacial flow of bubbles

High-quality Co products are desirable for a variety of applications due to its unique properties. Herein, an interfacial field of flowing bubbles was used to modify the microstructure of Co deposits in the electrowinning process. The effect of flowing bubbles on morphology, crystallographic structure and impurities of Co deposits were investigated. The nucleation and growth of Co deposits were discussed based on chronoamperometric experiments and sampling experiments. The results indicated that the microstructure of Co deposits was effectively modified by an external field of flowing bubbles. The Co deposits prepared in a quiescent electrolyte were porous and inhomogeneous, while the deposits prepared by using the flowing bubbles were compact and uniform. The nucleation and growth modes of Co deposits were also altered by the flowing bubbles. Preferentially oriented grains in the (110) direction were formed by instantaneous nucleation and screw dislocation growth of the deposits. Improvements in microstructure and crystallographic orientation were able to enhance the purity of Co deposits.

Next-gen approach to the combined micro/macro-scopic measurements of crystal growth in chalcogenide thin films: The case of Se90Te10

Crystal growth in 1 µm Se90Te10 thin films deposited on a variety of substrates was studied by means of a novel combination of direct microscopic and calorimetric measurements. Differential scanning calorimetry (DSC) was used to explore the macroscopic manifestation of the crystal growth in as-deposited Se90Te10 thin films, revealing the native-like crystal growth behavior (very close to that of the bulk glass) in the films deposited on the polymeric foil. The optical microscopy determined the following sequence for the crystal growth rates ur in the thin films deposited on different substrates: urwhite glass> urSiO2 glass> >urKapton. This finding is perfectly consistent with the calorimetric data, and can be explained by the combined influences of the Na+ ions migrating from the white glass substrate to the thin film/substrate interface, and by the compressive stresses arising from the large difference between the thermal expansion coefficients of Se90Te10 and the inorganic glasses. Conformation of the calorimetric and microscopic data was validated by the description of both datasets in terms of a single set of parametrized equations based on the combination of the temperature-resolved screw-dislocation growth model and the macroscopic nucleation-growth model. The novel approach to the crystal growth research in chalcogenide thin films was introduced, demonstrating its unprecedented accuracy, robustness and overall comprehension. All major aspects of this novel approach were discussed in detail, including the necessity to consider not only the substrate properties but also the associated process of structural relaxation that may significantly alter the crystal growth near glass transition.

The Origin and Formation Mechanism of an Inclined Line‐like Defect in 4H‐SiC Epilayers

An inclined line-like defect in 4H-SiC epilayers originates from a threading screw dislocation intersecting the surface, and its orientation is controlled by the sign of the Burgers vector of the dislocation. The defect forms through the interaction of local spiral-growth associated with the threading screw dislocation and step-flow growth related to the substrate off-cut. For further details see article number 2100512 by Jawad Ul Hassan and co-workers.

Study on burgers vector of dislocations in KDP (010) faces and screw dislocation growth mechanism of (101) faces.

We modified the conventional etching-optical method to measure dislocation direction in a KDP crystal. As burgers vector of dislocation in the KDP crystal must match the minimum periodic vector of the crystal lattice, we suggest that dislocations with a burgers vector of [101], [102] and [103] exist. Atomic force microscopy was employed to characterize the morphology of growth spirals on the hillock of (101) faces. Multi-spirals consisting of more than two element steps with a height of 0.5 nm which is equal to (101) face interplanar distances were observed. We propose the multi-spiral structure is determined by the burgers vector of the corresponding dislocation, and constructed a geometric model of the crystal with screw dislocation to derive the relationship. Growth spirals on the (101) face present a particular triangular morphology and we proved that the triangle structure is formed by connected steps in the 1/2[111] and [010] direction. Micropipes form when the magnitude of the dislocation's burgers vector exceeds 1 nm, as predicted by BCF theory. Interaction between dislocations was observed also.

Supramolecular Hexagonal Platelet Assemblies with Uniform and Precisely-Controlled Dimensions.

Geometric structures are commonly encountered in natural and designed systems. However, the bottom-up fabrication of regular geometric assemblies with precise dimensional control, especially from soft materials, poses an outstanding challenge in contemporary materials science and chemistry. Herein, we present a general method for the preparation of colloidally stable, hexagonal platelets via the formation of crystalline inclusion complexes of tris-o-phenylenedioxycyclotriphosphazene and block copolymers bearing interactive blocks. Dictated by the screw dislocation growth of inclusion complexes, uniform hexagonal platelets with precisely controllable dimensions can be prepared. This supramolecular assembly approach is further utilized to produce concentric hexagonal platelets via stepwise seeded growth from various inclusion complexes.

Uncovering the action of ethanol controlled crystallization of 3,4-bis(3-nitrofurazan-4-yl)furoxan crystal: A molecular dynamics study

A computational strategy in consideration of attachment energy, temperature, solubility and supersaturation unravels details of the solvent effect on the crystal morphology. The crystal morphologies were predicted by the advanced screw dislocation growth model. This research sheds much light on the crystal growth mechanisms with the example of 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF) in ethanol. The solvation model based on the experiment situation was established into periodic supercell. Molecular dynamics simulation was performed for obtaining the adsorption energy at the equilibrium state of the interface layer. The growth characteristics of relevant growth faces are introduced. At the same time, a periodic bond chains analysis can be applied to the existence and evolution of crystal growth units. The prediction results are in remarkable agreement with the experimental results. We found that crystal morphology of DNTF is composed of (002), (111), (111¯) and (101) faces in ethanol. As the saturation temperature rises, the (101) face becomes smaller and eventually disappears.

Formation of high crystalline LDH sludge for removing Cu and Zn from wastewater by controlled double-jet precipitation.

In order to improve the heavy metal wastewater treatment by avoiding formation of amorphous sludge phase, we develop a faster formation of high crystalline layered double hydroxide (LDH) sludge to remove Cu and Zn from wastewater by controlled double-jet precipitation (CDJP) without hydrothermal or heat aging post-treatment. A series of experimental procedures are conducted to determine the optimal parameters. Results show that the optimal adding rate, pH value, and stirring rate is 0.5mLmin-1, 9.0, and 500rpm, respectively. The CuZnAl-LDH phase sludge is formed in a well-crystallized hexagonal platelet, which assembled into a flower-like architecture. Comparative studies show that the formation of amorphous LDH sludge in conventional precipitation (CP) could be divided roughly into two stages-from the mixed copper hydroxide, zinc hydroxide, and scarbroite to the mixed low crystallinity CuAl-LDH and ZnAl-LDH. However, in CDJP method, the high crystalline LDH sludge evolved from a new four-step evolution process that is the formation of an amorphous (quasi-)multinary metastable ternary CuZnAl-LDH phase, followed by the indiffusion of cations and substitution of anions to fabricate crystalline LDH, the integrated LDH hexagonal platelets assembled into a flower-like architecture by the screw dislocation growth mechanism, the coarsening growth of each ternary LDH platelet, respectively. Thereinto, the formation of (quasi-)multinary metastable LDH phase instead of metal hydroxide in initial stage would be an obvious advantage of the CDJP method compared to CP method due to the former skipping the sequential precipitation.

One‐step synthesis of coral‐like high‐entropy metal carbide powders

AbstractThe synthesis of high‐entropy metal carbide powders is critical for implementing their extensive applications. However, the one‐step synthesis of high‐entropy metal carbide powders is rarely studied. Herein, the synthesis possibility of high‐entropy metal carbide powders, namely (Zr0.25Ta0.25Nb0.25Ti0.25)C (ZTNTC), via one‐step carbothermal reduction was first investigated theoretically by analyzing chemical thermodynamics and lattice size difference based on the first‐principle calculations, and then the ZTNTC powders with particle size of 0.5‐2 μm were successfully synthesized experimentally. The as‐synthesized powders not only had a single rock‐salt crystal structure of metal carbides, but also possessed high‐compositional uniformity from nanoscale to microscale. More interestingly, they exhibited the distinguished coral‐like morphology with the hexagonal step surface, whose growth was governed by a classical screw dislocation growth mechanism.

Chemical vapor deposition growth of sub-centimeter single crystal WSe2 monolayer by NaCl-assistant

Monolayer WSe2 exhibits unique optical and electronic properties, showing great potential applications in functional integrated devices, such as electronic devices and optoelectronics. Understanding the growth behavior and process are the key points for the salt-assisted growth of large domain WSe2 monolayers, it is also very important for its further application in on-chip laser and opto-devices. Here, we report a NaCl-assistant method for controlled growth of single crystal monolayer WSe2 with a domain size up to 0.57 mm on SiO2/Si substrate. Atomic-resolution scanning transmission electron microscopy reveals that the Se1 and Se2 vacancy point defects are the main defect type of those materials. The growth behavior of the salt-assisted method have been systemly investigated. The loading mass of NaCl powder prefers to be less with the controllable vapor process. The flow of hydrogen gas was also preferred to be suitable with a weak etching effect. The morphology of monolayer WSe2 shows a sensitive temperature dependence evolution with the growth temperature increasing. A screw dislocation growth behavior with 15° angle is also observed with the NaCl-assistant method. The results provide a deep understanding of the mechanism for the NaCl-assistant growth of large size monolayer WSe2.

Morphological control and kinetics in three dimensions for hierarchical nanostructures growth by screw dislocations

The precise control and in-depth understanding of the anisotropic crystal screw dislocation growth could yield further optimization of nanomaterial design and broader applications, yet the studies of rational control and kinetics for more complex nanostructures are still insufficient. In this work, by programming synthesis conditions, we achieve a controllable three-dimensional (3D) screw dislocation growth of hierarchical nanostructures, including nanowires, nanoplates, and previously unreported hierarchical hollow nanobelts, via a facile chemical vapor deposition approach. Notably, the screw dislocation growth in nanobelts is confirmed by the clear observations of the stepwise spiral terraces with initial hexagonal to octagonal shapes and the hollow cores in the growth spiral centers, as well as the fundamental Burton-Cabrera-Frank crystal growth theoretical calculations. The formation of the nanowires and nanoplates can be well interpreted by the previously reported screw dislocation growth model, while a new 3D screw dislocation growth model with considering of transition in growth velocities and directions is proposed to interpret the formation of the nanobelts and other potential complex nanostructures. This study not only enriches our understanding of the screw dislocation growth kinetics but also guides us to achieve the precise morphological design and control in nanosynthesis.

Screw dislocation assisted spontaneous growth of single-crystalline α-Al2O3 microrods

Abstract Herein we reported a simple chemical vapor deposition approach to synthesize single crystal α-Al 2O3 microrods with diameters of 2–4 μm and lengths of 10–30 μm on the as-prepared SiC-Si-Al2O3 ceramics based on the screw dislocation growth. Two types of evidence for screw dislocation growth have been conclusively observed in the as-synthesized microrods: scanning electron microscopy analysis reveals that the representative morphology feature of the screw dislocation growth is the stepwise spiral terrace configuration and the growth kinetics of the as-synthesized microrods follows the prediction of the dislocation growth mechanism as described by Burton-Cabrera-Frank theory. This work provides not only a new method for synthesizing Al 2O3 microrods but also a new insight into the growth mode for Al2O3 microrods.

Polymorphic Smooth Interfaces Formation Based on the Biphasic BaTeMo2O9 Using Top Multi-Seeded Growth

An interesting phenomenon of two polymorphic heterojunctions is reported in this paper. The selective growth of the individual phases of high-quality α- and β-BaTeMo2O9 (BTM) crystals was successfully achieved using an optimized flux system and growth parameters. A biphasic BTM crystal based on a multiseeding technique used to control the nucleation and subsequent growth was realized in a one-flux system. The formation of a grain boundary, similar to a heterojunction, between the α- and β-BTM crystals emerged as an unavoidable consequence of this process, and the factors that led to the formation of the grain boundaries in the multiseeds were examined. Lattice mismatch and interfacial binding energy calculation verified that the BTM crystals were grown together rather than being physically adhered, and the chains at the grain boundary were linked by O5Mo–O–MoO5 dioctahedrons corner-sharing O atoms at the eutectic boundary. The screw dislocation growth mechanism was confirmed for β-BTM with the growth unit...

Spontaneous growth of hexagonal ZrB2 nanoplates driven by a screw dislocation mechanism

Hexagonal ZrB2 nanoplates had been successfully synthesized by a facile molten-salt assisted borothermal reduction technique based on the screw dislocation growth mechanism for the first time.

Crystal growth and viscous flow in barium disilicate glass

Decoupling between the diffusion coefficients that control crystal growth (DU) and viscous flow (Dη) in deeply supercooled glass-forming liquids is one of the most celebrated, still unsolved, phenomena in glass science because it strongly impacts the analysis and prediction of crystallization kinetics. To further understand the decoupling phenomenon, we measured viscosity and crystal growth rates (of the crystalline surface layer growth and internally nucleated crystals) of a supercooled liquid with barium disilicate composition. We performed all measurements using glass samples from the same batch, a rare case that we call a “clean” experiment. This type of analysis is uncommon, and its aim is to minimize the uncertainty due to the composition variation that is inherent in laboratory glass production. The decoupling temperature (Td), the glass transition temperature (Tg), the melting point (Tm), and the liquid fragility index were obtained and successfully used to test a recently derived relationship which allows one to estimate Td by knowing only Tm and the viscosity curve. We also show, for the first time, that the reduced decoupling parameter, which gauges the degree of deviation between DU and Dη, does not depend on the crystal growth mechanism for the cases of Normal or Screw Dislocation growth.

Microstructure and texture evolution of electrodeposited coatings of nickel in the industrial electrolyte

Nickel is an important strategic metal material, which has been widely used in modern industry. The different electrolyte systems and main parameters have a great effect on microstructure and mechanical properties of electrodeposited coatings. In order to investigate the evolution of texture and preferential orientation of nickel electro-crystallization in sulfide nickel soluble anode/sulfate solution, and grain size, microstructure of electrodeposited coatings of nickel were characterized by electrochemical workstation, XRD and SEM methods.The results show that nickel electro-crystallization conforms to the classical nucleation theory and crystal growth theory. The preferential orientation of electrodeposited coatings of nickel can be changed initially from (111) and (200) planes to (220) plane after 16h. The surface morphology changes slowly from pyramid to cellular structure, while the growth mechanism changes from screw dislocation growth to cumulative growth model. The cross sectional microstructure of electrodeposited coatings is non-uniform and mostly grains are columnar and perpendicular to the sheet. The distribution of grains abides by stepwise distribution along the thickness. The microstructure of electrodeposited coatings is fine equiaxed grain region and coarse columnar grain region, which are perpendicular to starting sheet when the electrodeposition time is 144h. Angle grain boundary is related to grain size, whereas the coincidence site lattice (CSL) is associated with preferential orientation. Therefore the grain boundary misorientation are mainly above 15°, being more than angle grain boundaries and coincidence site lattice Σ3 appearing highest frequency.

Characterization of screw dislocation-driven growth in nickel micro-nanostructure electrodeposition process by AFM

In this study, nickel coating with micro-nanostructure feature was fabricated by a simple two-step method during electrodeposition process. To evaluate surface morphology characteristics, the histogram and power spectral density analyses of atomic force microscopy data were extracted from two different morphologies of nickel films. Results showed that boric acid plays an important role in the control of nucleation and the growth of micro-nanostructures. With clear observation of growth steps in atomic force microscopy characterization, terrace width and spiral growth proved the existence of screw dislocation growth.

Engineer in Situ Growth of α-Al2O3 Whiskers by Axial Screw Dislocations

Screw dislocation growth mechanism has recently drawn much attention in the micro/nanostructures due to its unique existence conditions and impact on the morphology. Here we reported the observation of a screw dislocation growth of single crystal α-Al2O3 whiskers via a facile and novel in situ synthesis method. By programming synthesis temperatures, we observed an interesting circular to polygonal thread morphology transition on the surface of the as-synthesized α-Al2O3 whiskers. Clear observations of the terraces and the axial dislocations under SEM and TEM characterizations revealed the presence of screw dislocation growth in the as-grown α-Al2O3 whiskers. This mechanism was further validated by analyzing both the supersaturation of the system and the thermodynamics of chemical reaction in the system. This strategy provides a detailed understanding of the screw dislocation growth in the Al2O3 whiskers as well as a new strategy for engineering Al2O3 whiskers.